Mercedes-Benz CL65 AMG

Here we were thinking the supercharged V-8 was strong.

The Mercedes-Benz relationship with its performance partner, AMG, is a classic Jekyll-and-Hyde, good-cop/bad-cop situation. Whereas Mercedes-Benz has to demonstrate a fair bit of corporate responsibility, AMG is pretty much free to explore over-the-top concepts.

Such as this CL65 AMG. Fitted with a bored-and-stroked high-pressure-turbocharged version of the V-12 engine found in the stock CL600, the coupe produces 604 horsepower and a rib-cage-flattening 738 pound-feet of torque between 2000 and 4000 rpm. Expressed in metric terms, the torque output is a round 1000 newton-meters of drivetrain-twisting force.

The really funny part of all of this is that the output had to be reduced somewhat in the interest of transmission life. There is another 200 or so newton-meters to be had here, and the aftermarket loonies will undoubtedly go looking for it. But Mercedes-Benz will not warrant that kind of exploration, even though this AMG car is covered by the Mercedes warranty with no transmission upgrades beyond new clutch discs and revised control logic. There are, however, beefed-up driveshafts and hubs farther downstream.

To get this kind of urge, AMG increased the cylinder bore by 0.6 millimeter and lengthened the stroke by six, ending up with 5980cc of engine displacement. AMG-spec forged pistons with thicker wrist pins fit inside the new holes, where they are cooled by an upgraded oil-spray system.

The combustion chambers were reshaped for a 9.0:1 compression ratio, and the intake camshafts have higher lift and longer dwell. Both turbochargers have larger housings and wheels and pump nearly 22 pounds of boost via a front-mounted air-to-water intercooler that is about 70 percent larger than the stock item.

According to AMG engineers, this results in a 25-percent reduction in intake-air temperature at full load. Naturally, the electronic engine-management system had to be reconfigured for every aspect of operation, including those revised waste-gate pop-off parameters. A redesigned aluminum and carbon-fiber-reinforced-plastic engine cover enlightens any bystanders who somehow have missed the prominent AMG and V-12 biturbo badges adorning the bodywork.

Drivers need no such reminders. Even if they ignore the AMG letters on the big electroluminescent speedometer that reaches to the 360-kilometer-per-hour mark (U.S. cars will probably get a 240-mph gauge), the first full-throttle excursion will likely prompt involuntary Anglo-Saxon expletives containing more letters than the storied initials of this in-house tuner.

Despite completely revamped electronic oversight of the power delivery (ABS, ASR, and ESP, plus-we suspect-torque-moderating strategies in low gears), the sheer thrust put down through the 9.5-inch-wide split-spoke rear alloy rims and their meaty 275/35ZR-19 Michelin Pilot Sport tires is mind-boggling. Even to jaded auto writers used to Vettes and the like, the surge comes as a big surprise.

While driving AMG's test course along the Route Napoléon above France's Côte d'Azur in the Maritime Alps, we had frequent occasion to pass slower cars on the short straights that connect this serpentine roadway. We soon discovered the need to exercise great care with the throttle lest we end up hurtling into curves at unreasonably high velocities.

Punch the pedal to pass, and a second later the target car is backing past the right-side windows as if it had just popped a parachute. Even with the engine and transmission controls striving to smooth all of this out, an abrupt driver can produce rapidly alternating fore-and-aft accelerations, and care has to be taken to avoid them.

But after a few deep digs at the throttle, resulting in multiple downshifts and eyeball-depressing launches toward the horizon, a driver learns to simply squeeze the throttle for a pass. With more than 700 pound-feet of torque twirling the rear wheels anywhere between 2000 and 4000 engine revs, downshifts are not necessary. It's just a matter of toeing the pedal and wafting away on a smooth wave of energy.

The sound emanating from the four AMG tailpipes is entirely in concert with this avalanche of power, growing from a melodic burble to a hard snarl as the revs rise. Yet the overall refinement of the car meets the best patrician expectations, and the CL65 rides and shifts smoothly, with interior noise levels that almost belie its colossal performance potential.

The ride is helped enormously by Mercedes-Benz's active-body-control system, which has been comprehensively recalibrated for its new role in the AMG car. Without having to restrain roll and pitch motions by conventional means, the engineers could strike a better ride-and-handling compromise while tuning the AMG-specific springs and struts. For a 4800-pound coupe, the CL65 has moves in the mountains that will surprise Porsche drivers. As will its braking. The front rotors are 15.4-inch units with eight-piston calipers.

Expected to cost $180,000 when it arrives in the U.S. next summer, the CL65 has every creature comfort and available option that Mercedes has on offer. What the CL65 will lack is availability. Only 400 will make it to this country during the two years it will be sold here, so don't say we didn't warn you.